A complex network of regulatory pathways control gene expression in eukaryotes. Environmental constraints, such as nutrient availability, mitogenic signals such as growth factors or hormones, as well as developmental cues such as the transition from vegetative to reproductive, modulate transcription and translation in plants. Genes which are involved in this modulation can be introduced into a plant and used to affect phenotype in adventitious or desirable ways.
The development of methods for the introduction of foreign genes into organisms has had a profound impact on fields of medicine and agriculture and has further expanded understanding of regulatory mechanisms involved in gene expression. While the movement of genes within plant species or between closely related plant species by traditional methods based on sexual reproduction has played an important role in crop improvement for most of this century, the pace of crop improvement by such methods has been slow and limiting due to the reliance on naturally occurring genes. Recent advances in the field of genetic engineering have led to the development of genetic transformation methods that allow the introduction of recombinant DNA into organisms. The recombinant DNA methods which have been developed have greatly extended the sources from which genetic information can be obtained for crop improvement. Recently, new crop plant varieties, developed through recombinant DNA methods, have reached the marketplace. Genetically engineered soybeans, maize, canola, cotton and other crops are now widely utilized by North America farmers.
Genes from plants and other entirely unrelated organisms are being cloned, genetic regulatory signals are being deciphered, and genes conferring new traits, are being transferred. Introduction of single genes or of combinations of genes through stacking pose challenges in controlling the expression of the transferred genes. Many of the recent advances in plant science have resulted from application of the analytical power of recombinant DNA technology coupled with plant transformation and an understanding of gene regulatory processes. These approaches facilitate studies of the effects of specific gene alterations and additions on plant development and physiology and make possible the direct manipulation of genes to bio-engineer improved plant varieties.
While some success has already been achieved in improving crop plants through the introduction and regulation of recombinant DNA, the progress of genetic engineers working to improve many important crop species is impeded by inefficient methods and limited choices of gene regulation in crop plants. Thus, improved methods for controlling gene expression in plants and the transformed plants regenerated there from are desired.